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  • 1
    Electronic Resource
    Electronic Resource
    Growth and alkaloid contents in leaves of Tabernaemontana pachysiphon Stapf (Apocynaceae) as influenced by light intensity, water and nutrient supply (1996)
    Springer
    Oecologia 107 (1996), S. 160-169 
    Details
    ISSN: 1432-1939
    Keywords: Monoterpene indole alkaloids ; Tropical trees ; Abiotic factors ; Growth ; C/N balance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The growth of Tabernaemontana pachysiphon (Apocynaceae) plants and the alkaloid content of leaves were investigated in the greenhouse at three levels of nutrient supply under two contrasting water and light regimes. We determined height increment, above-ground biomass production, leaf size, specific leaf weight and the content of the alkaloids apparicine, A2, isovoacangine, tubotaiwine and tubotaiwine-N-oxide. The effects of major controlling factors such as light, water and nutrient supply could be directly correlated with growth and were largely independent of each other. In contrast, leaf-alkaloid contents were influenced by interdependencies among the main factors and individually affected in a synergistic or antagonistic manner which deviated from the effects on growth. The following general trends could be identified with respect to the quantitatively predominant alkaloids apparicine, tubotaiwine and isovoacangine. Increasing nutrient supply had a positive effect on both growth and alkaloid content. Drought increased alkaloid content, but retarded growth. High light intensity lowered alkaloid content but promoted growth. We investigated the relationship between primary production and the production of secondary metabolites with respect to relative and total alkaloid content as well as in relation to the leaves' nitrogen status. Our results showed that under conditions of low nutrient supply, higher proportions of leaf nitrogen were allocated to alkaloids than at moderate or high nutrient supply. Under conditions of drought and low light, all plants allocated almost equal proportions of leaf nitrogen to alkaloids, regardless of fertiliser. Total alkaloid content per plant, however, increased with fertilisation. With respect to the N-allocation strategy, we found no indication of a trade-off between primary production and the production of secondary metabolites in this species. Rather, our results are in accordance with the carbon nutrient balance hypothesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00327899
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  • 2
    Electronic Resource
    Electronic Resource
    Carbon dioxide assimilation and stomatal response of afroalpine giant rosette plants (1985)
    Springer
    Oecologia 65 (1985), S. 207-213 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Maximal rates of CO2 assimilation of 8–11 μmol m-2 s-1 at ambient CO2 concentration were measured for Dendrosenecio keniodendron, D. brassica, Lobelia telekii and L. keniensis during the day in the natural habitat of these plants at 4,200 m elevation on Mt. Kenya. Even at these maximal rates, the CO2 uptake of all species was found to correspond to the linear portion of the CO2 response curve, with a calculated stomatal limitation for CO2 diffusion of 42%. Photosynthesis was strongly reduced at temperatures above 15° C. In contrast to this sensitivity to high temperatures, frozen leaves regained full photosynthetic capacity immediately after thawing. Stomata responded to dry air, but not to low leaf water potentials which occurred in cold leaves and at high transpiration rates. During the day reduced rates of CO2 uptake were associated with reduced light interception due to the erect posture of the rosette leaves and with high temperatures. Stomata closed at vapour pressure deficits which were comparable in magnitude to those characteristic of many lowland habitats (40 mPa Pa-1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379219
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of supercooling and freezing on photosynthesis in freezing tolerant leaves of Afroalpine ‘giant rosette’ plants (1987)
    Springer
    Oecologia 72 (1987), S. 366-371 
    Details
    ISSN: 1432-1939
    Keywords: Chlorophyll fluorescence ; Supercooling ; Frozen leaves ; Photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The effect of supercooling and freezing on the photosynthetic capability of representatives of the permanent frost hardy giant rosette plants Dendrosenecio keniodendron, D. brassica and Lobelia telekii, of the tropical alpine regions was investigated with the non-invasive chlorophyll a fluorescence technique. While supercooling, normal chlorophyll a fluorescence kinetics exhibiting the sequence 0, I, (D), P, S, M, were recorded, however with some retardation of both, the fast and the slow characteristics as compared to those obtained at day-time temperature. As long as the leaves remained unfrozen, the rise of the variable fluorescence F ν from the level 0 to P was inversely related to a drop of the temperature from about 0°C to-8°C. The increase of F ν with lower temperature is understood to result from a decrease of the velocity of the quenching reactions while photoreduction of the primary electron acceptor appeared to be unimpeded. The second fluorescence maximum (M), usually interpreted to indicate the commencement of the biochemical reactions of photosynthesis was consistenly to be observed during supercooling. Fluoescence induction kinetics of frozen leaves showed only fast rise to presumably F max which was not followed by a significant decay for as long as 4 min. The lack of substantial quenching indicates that in the freeze-dehydrated state neither reoxidation of the primary acceptor nor energetization of the thylakoid membrane was accomplished. This effect however was immediately and fully reserved upon thawing of the leaves when the usual fluorescence induction kinetics as well as normal rates of CO2-uptake were observed. Thus the permanent frost-hardy afroalpine plants do not exhibit any even short-term memory effect of the nocturnal frost on such a delicate process as is photosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377565
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  • 4
    Electronic Resource
    Electronic Resource
    Frost hardening and photosynthetic performance of Scots pine (Pinus sylvestris L.). II. Seasonal changes in the fluidity of thylakoid membranes (1998)
    Springer
    Planta 204 (1998), S. 201-206 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Electron paramagnetic resonance ; Frost hardening ; Membrane fluidity ; Photoperiod ; Scots pine ; Thylakoid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The fluidity of chloroplast thylakoid membranes of frost-tolerant and frost-sensitive needles of␣three- to four-year-old Scots pine (Pinus sylvestris L.) trees, of liposomes produced from the lipids of the thylakoids of these needles, and of liposomes containing varying amounts of light-harvesting complex (LHC) II protein was investigated by means of electron paramagnetic resonance (EPR) measurements using spin-labelled fatty acids as probes. Broadening of the EPR-resonance signals of 16-doxyl stearic acid in chloroplast membranes of frost-sensitive needles and changes in the amplitudes of the peaks were observed upon a decrease in temperature from +30 °C to −10 °C, indicating a drastic loss in rotational mobility. The lipid molecules of the thylakoid membranes of frost-tolerant needles exhibited greater mobility. Moderate frost resistance could be induced in Scots pine needles by short-day treatment (Vogg et al., 1997, Planta, this issue), and growth of the trees under short-day illumination (9 h) resulted in a higher mobility of the chloroplast membrane lipids than did growth under long-day conditions (16 h). The EPR spectrum of thylakoids from frost-tolerant needles at −10 °C was typical of a spin label in highly fluid surroundings. However, an additional peak in the low-field range appeared in the subzero temperature range for the chloroplast membranes of frost-sensitive needles, which represents spin-label molecules in a motionally restricted surrounding. The EPR spectra of thylakoids and of liposomes of thylakoid lipids from frost-hardy needles were identical at +30 °C and −10 °C. The corresponding spectra from frost-sensitive plants revealed an additional peak for the thylakoids, but not for the pure liposomes. Hence, the domains with restricted mobility could be attributed to protein-lipid interactions in the membranes. Broadening of the spectrum and the appearance of an additional peak was observed with liposomes of pure distearoyl phosphatidyl glycerol modified to contain increasing amounts of LHC II. These results are discussed with respect to a loss of chlorophyll and chlorophyll-binding proteins in thylakoids of Scots pine needles under winter conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050247
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  • 5
    Electronic Resource
    Electronic Resource
    Frost hardening and photosynthetic performance of Scots pine (Pinus sylvestris L.) needles. I. Seasonal changes in the photosynthetic apparatus and its function (1998)
    Springer
    Planta 204 (1998), S. 193-200 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Chlorophyll ; Chlorophyll-binding protein ; Frost hardening ; Photosynthesis ; Pinus (frost hardening)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Photosynthetic CO2 uptake, the photochemical efficiency of photosystem II, the contents of chlorophyll and chlorophyll-binding proteins, and the degree of frost hardiness were determined in three-year-old Scots pine (Pinus sylvestris L.) trees growing in the open air but under controlled daylength. The following conditions were compared: 9-h light period (short day), 16-h light period (long day), and natural daylength. Irrespective of induction by short-day photoperiods or by subfreezing temperatures, frost hardening of the trees was accompanied by a long-lasting pronounced decrease in the photosynthetic rates of one-year-old needles. Under moderate winter conditions, trees adapted to a long-day photoperiod, assimilated CO2 with higher rates than the short-day-treated trees. In the absence of strong frost, photochemical efficiency was lower under short-day conditions than under a long-day photoperiod. Under the impact of strong frost, photochemical efficiency was strongly inhibited in both sets of plants. The reduction in photosynthetic performance during winter was accompanied by a pronounced decrease in the content of chlorophyll and of several chlorophyll-binding proteins [light-harvesting complex (LHC)IIb, LHC Ib, and a chlorophyll-binding protein with MW 43 kDa (CP 43)]. This observed seasonal decrease in photosynthetic pigments and in pigment-binding proteins was irrespective of the degree of frost hardiness and was apparantly under the control of the length of the daily photoperiod. Under a constant 9-h daily photoperiod the chlorophyll content of the needles was considerably lower than under long-day conditions. Transfer of the trees from short-day to long-day conditions resulted in a significantly increased chlorophyll content, whereas the chlorophyll content decreased when trees were transferred from a long-day to a short-day photoperiod. The observed changes in photosynthetic pigments and pigment-binding proteins in Scots pine needles are interpreted as a reduction in the number of photosynthetic units induced by shortening of the daily light period during autumn. This results in a reduction in the absorbing capacity during the frost-hardened state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050246
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  • 6
    Electronic Resource
    Electronic Resource
    Factors influencing hydrocarbon degradation in three freshwater lakes (1985)
    Springer
    Microbial ecology 11 (1985), S. 127-137 
    Details
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mixed microbial flora of 3 lakes in Ohio with differing histories of hydrocarbon pollution was examined in relation to the ability to use hydrocarbons. Weathered kerosene was spiked with naphthalene, pristane, 1,13-tetradecadiene, andn-hexadecane and added to water-sediment mixtures from the 3 lakes, and utilization of the 4 marker hydrocarbons was measured. Each of the marker hydrocarbons was metabolized; naphthalene was the most readily used and pristane was the most resistant. Values for dissolved oxygen suggest that oxygen did not limit hydrocarbon degradation in the water column at any site examined. Nutrient addition studies indicated that nitrogen and phosphorus limited hydrocarbon degradation at all sites examined. Maximum numbers of heterotrophic bacteria were detected when the water temperature was 10°C or higher. The data indicate that temperature limits hydrocarbon degradation in the winter, except at a site which had been impacted by an oil spill and which received chronic inputs of hydrocarbons and nutrients. In samples from that site, all 4 marker hydrocarbons were degraded at 0°C. Results of temperature and nutrient-addition experiments suggest that different seasonal populations of hydrocarbon users are selected at that site, but not at other lake sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02010485
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  • 7
    Electronic Resource
    Electronic Resource
    Reassessment of root competition for P of field-grown maize in pure and mixed cropping (1988)
    Springer
    Plant and soil 106 (1988), S. 299-301 
    Details
    ISSN: 1573-5036
    Keywords: lupin ; maize ; phosphate ; root competition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Root competition for phosphate (P) in the field was calculated with maize i) as singly grown plants, ii) in pure cropping and iii) in mixed cropping with lupin. The experimentally determined parameters used for this purpose were thein situ root-distance pattern as registered by autoradiography and the P-depletion cylinder around a maize root as determined autoradiographically under radial diffusional flow. The results do not indicate any competition for P between roots of adjacently grown plants in either pure or mixed cropping. On the other hand, the P-depletion cylinders of approximately one third of the roots of an individual maize plant were found to overlap. However, when allowance was made for the concentration gradients within a depletion cylinder, the actual competition for phosphate was less than 1%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02371230
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  • 8
    Electronic Resource
    Electronic Resource
    Development and replenishment of the P-depletion zone around the primary root of maize during the vegetation period (1987)
    Springer
    Plant and soil 101 (1987), S. 247-255 
    Details
    ISSN: 1573-5036
    Keywords: freeze-cutting ; dynamics ; depletion zone ; root longevity ; maize ; P-deficiency ; phosphate ; radioautography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The dynamics of the development and replenishment of P-depletion zones around the primary root of maize (Zea mays L. cv ‘Garbo’) was studied during a vegetation period (80 days) under greenhouse conditions in a loamy sand of low P-availability. A recently described freeze-cutting technique was used to determine radial diffusion of labelled phosphate to the primary root. The development of the depletion zone was biphasic. In the initial phase after two days of growth of the primary root in a soil layer labelled with33P a minimum of isotopically exchangeable P (EP) was observed which had decreased to about 30% of its original amount at the root surface. At that time the corresponding P-concentration in the soil solution was calculated to be as low as 5×10−7 M. The depletion zone had already spread 0.4 mm from the root surface. During the second phase, between the 10th and 20th day of plant growth the concentration of EP at the root surface increased slowly but did not change markedly. However, the depletion zone continued to spread and after the 20th day of growth reached its maximal diameter (1.07 mm from the root surface) but remained completely within the root hair cyclinder; the single root hairs never exceeded 1.14 mm in length. The biphasic growth of the depletion zone was probably caused by proton extrusion of the root tip. Acidification of the soil solution from pH 5.8 to about 3.9 results in an about 3-fold rise of the concentration of desorbed phosphate and might also have activated acidophilic P-translocators of the root during the initial phase. Anion over cation uptake normally prevailing during the later stage of root development might resulted in a rise of the soil pH within the root hair zone. Consequently P-availability, as well as P-uptake capacity declined, but P-uptake by the seminal root still continued until the 20th day. Subsequently, the P-concentration within the depletion zone increased again while simultaneously its extent was reduced until it was almost completely replenished after 60 days indicating a loss of P-uptake capacity of the primary root. Within the root tissue33P was accumulated to about twice the concentration of that in the undepleted soils. This accumulation corresponded to periods of high uptake due to the development of root laterals. In the root cortex a high P-content was observed during the first 30 days of growth. At the onset of the reproductive stage of the plant the P-content of the shoot and especially in the developing seeds rose considerably at the cost of phosphate stored in the root cortex. The accumulation of33P in the root tissue indicated that nutrient gain was mainly achieved during the early stages of plant development and that P was temporarily stored to some extent within the root system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02370652
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  • 9
    Electronic Resource
    Electronic Resource
    High-spin spectroscopy of168Hf (1987)
    Springer
    The European physical journal 327 (1987), S. 397-402 
    Details
    ISSN: 1434-601X
    Keywords: 21.10.Re ; 23.20.Lv ; 27.70.+ q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The nucleus168Hf was studied up to spin (38+) in the yrast band and to spins (41−) and (38−) in the lowest two negative-parity bands. The onset of a proton alignment (h9/2 or i13/2 quasiparticles) is observed in these three bands for the highest transitions. A new band with even spins and negative parity was found. The interaction strength between the ground-state band and theAB band is measured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01289564
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  • 10
    Electronic Resource
    Electronic Resource
    High-spin spectroscopy of162Hf (1988)
    Springer
    The European physical journal 329 (1988), S. 289-299 
    Details
    ISSN: 1434-601X
    Keywords: 21.10.Re ; 23.20.Lv ; 27.70.+q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Excited states in162Hf were investigated up to spinI ≈ 38 using the anti-Comptonspectrometer array HERA with 21 detectors. In addition, some information was obtained on161Hf. The analysis of triple coincidences was crucial for the construction of the level schemes. The results are interpreted within the framework of the cranked shell model and are compared to neighbouring isotopes and isotones, showing Fermi level and deformation effects. The systematic behaviour of the band crossings in the Hf isotopes and theN=90 isotones is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01290234
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